New Gold vs Ancient Copper

How close are they?

ΔE 23.2, loose: different enough that you should pick on purpose. Ancient Copper is a little lighter, much more saturated, warmer than New Gold.

Can I use Ancient Copper instead of New Gold?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 23). Ancient Copper is a little lighter, much more saturated, warmer than New Gold.

Can I use New Gold instead of Ancient Copper?

The same difference applies the other way round: New Gold is a little darker, much more muted, cooler.

ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.